When a flat panel display device or a semiconductor device is fabricated, a process for depositing a thin film, a photolithography process for exposing a region selected in the thin film, and an etching process for removing the thin film of the selected region are performed several times. Particularly, the photolithography process includes a coating process for forming a photosensitive film of photosensitive solution such as a photoresist on a substrate or a wafer, and an exposing and developing process for patterning the photosensitive film by using a mask with a predetermined pattern.
In general, a spray coating method, a roll coating method, a spin coating method, or the like, is used in the coating process for forming a photosensitive film on a substrate and a wafer.
Because the spray coating method and the roll coating method are not suitable to achieve high precision in the uniformity of a coating film and the adjustment of a thickness of the film, the spin coating method is used for high-precision pattern formation.
A spin coater used in the spin coating method will now be described in detail with reference to accompanying drawings.
FIG. 1 is a sectional view which illustrates the structure of a general spin coater.
As shown, the spin coater includes a spin chuck 5 that is connected to a rotating shaft 6. A cover 7 surrounds the spin chuck 5 and may be opened and closed. A nozzle 4 is placed above the spin chuck 5 and moves into the cover 7 when the cover 7 is opened.
An object 10 to be processed and coated with a photosensitive film is mounted on the spin chuck 5, and a drain valve (not shown) for discharging photosensitive solution, such as photoresist, to the outside is installed at a lower portion of the cover 7.
In order to form a coating film on the predetermined object 10, first, the nozzle 4 of the spin coater having the aforementioned structure is lowered and sprays photosensitive solution onto a surface of the object 10, which has been placed on the spin chuck 5.
When the photosensitive solution is sprayed onto the object 10, the cover 7 is hermetically closed, a motor (M) is rotated, and the rotating shaft 6 connected thereto is rotated, thereby rotating the spin chuck 5 with the object 10 a certain number of times.
When the spin chuck 5 is rotated, the photosensitive solution on the surface of the object 10 is spread out by a centrifugal force, thereby applying the photosensitive solution over an entire surface of the object 10.
After the photosensitive solution is applied over the entire surface of the object 10, the applied photosensitive solution is hardened. Then, a predetermined pattern is formed on the surface of the object 10 through exposure and development using a photo mask or the like.
Although the spin coating method using the spin coater is suitable to coat a small object such as a wafer with a photosensitive film, it is not suitable to coat a large and heavy substrate, such as a flat panel display device having a glass substrate for a liquid crystal display panel with a photosensitive film.
This is because it gets harder to rotate a substrate at a high speed as the substrate gets larger and heavier. Further, damage to the substrate can occur and a lot of energy is consumed when the substrate is rotated at a high speed.
Also, the spin coating method is disadvantageous in that a large amount of photosensitive solution is wasted in comparison with the amount of photosensitive solution used in the photolithography process. In particular, a considerable amount of photosensitive solution is dispersed outside the spin chuck at the time of high-speed rotation, and is wasted. Substantially, the amount of wasted solution is much larger than the amount of solution used for coating, and the dispersed photosensitive solution may form particles that contaminate following thin film forming processes. The particles can also cause environmental pollution.